Fresh-cut produce (including bagged salad, baby spinach, shredded, and sliced carrots, shredded lettuce and cabbage, diced and sliced onions, and other cut fruits and vegetables) is an approximately three billion dollar industry. Efficiently cleaning and processing fresh-cut produce is essential to product safety, product quality, and cost management. A significant portion of the cost of processing fresh-cut produce is related to (a) the amount of water used during the process, and (b) the cost of the chemicals (frequently chlorine) mixed with the water to produce a sanitizing liquid.
In current fresh-cut processing, harvested produce is generally cut and then washed to remove organic exudate (such as juices and/or a more viscous pulpy matter) that has leaked from freshly-cut surfaces, as well as field debris and soil particulates. This “organic exudate” reacts immediately and continuously with chlorine and other sanitizers, and consequently reduces the level of active (“free”) chlorine and other sanitizers in the washing solution. Free chlorine and other sanitizers can be replenished through the “make-up” addition of chemicals, but the continuing accumulation of organic material in the wash solution requires the addition of ever-larger amounts of sanitizer chemicals in order to maintain an adequate concentration of active sanitizer for sanitizing produce and preventing microbial cross-contamination.
When adequate sanitizer concentration is not maintained above a critical level, not only is the efficacy of microbial reduction diminished, but also microbial survival in wash water is enhanced, which allows microbial contamination of otherwise clean produce. This then results in significant food safety and food quality problems. Additionally, some by-products from chlorination reactions with organic exudate are known or suspected carcinogens, and the accumulation of large amounts of organic material in the wash water leads to increases in their rates of formation, and to higher residual levels in the final product. The presence of these by-products prompted the European Union to prohibit the use of chlorinated solutions for produce washing. Thus, early and effective removal of organic exudate is critical.
Effective microbial inactivation in fresh-cut produce washing depends on a number of factors, including sanitizer concentration, exposure time of the produce to the washing solution, and the degree of agitation and turbulence experienced by the produce. Sanitizer concentration and exposure time are important because there is a strong relationship between these factors and the desired outcomes, including microbial inactivation and maintenance of product quality.
If the combination of sanitizer concentration and exposure time is insufficient, inadequate microbial inactivation is achieved. On the other hand, if the combination of sanitizer concentration and exposure time is excessive, product damage will occur. Agitation and turbulence are also important because they break up “clumps” of produce and also reduce the thickness of the “stagnant” boundary layer on the produce surface through which the sanitizing agent must penetrate in order to be effective.
In the prior art, washing of fresh-cut produce is typically conducted in either a continuous, semi-batch, or batch process. In continuous processes, fresh-cut produce is either submerged in a washing solution that flows through a flume, or resides on a moving belt that is subjected to a sprayed washing solution. In the former case, the mean exposure time of the produce to the washing solution is given by the volume of the flume divided by the volumetric flow rate through the flume. In the latter case, the exposure time of each piece of produce is given by the length of the moving belt, divided by the linear velocity of the belt.
For spray washing on a belt, attempts to increase the exposure time require either a wider belt moving more slowly, or a longer belt. Since horizontal space is severely constrained in most of the fresh-cut processing facility in the United States, neither approach is a viable option. U.S. Pat. No. 9,326,543 to McEntire and U.S. Pat. No. 6,626,192 to Garcia disclose (primarily) spray-type systems where produce on a perforated conveyor is sprayed from both above and below the conveyor. Note that, although sprayers disclosed in the prior art are directed upwardly at the bottom of a produce conveyor, the sprayers are not positioned to directly spray produce as it falls downwardly through the air above the conveyor.
For flume washing, attempts to increase the exposure time require either more pieces of equipment, each with less throughput, or equipment with larger dimensions. U.S. Pat. No. 8,646,470 to Bajema is an example of a (primarily) flume type wash system.
Continuous-flume washing has several important limitations. First, to control the cost of water usage and the energy to chill the water, wash water in the flume system is often reused, leading to a significant accumulation of organic exudate along with field debris and soil particulates. The organic constituents react rapidly and chemically with chlorine, thereby reducing the amount of free chlorine. The accumulation of exudate and other contaminants also allows the formation of chlorinated by-products, and makes it difficult to maintain the chlorine concentration at a level sufficient to achieve microbial inactivation.
Second, reuse of process water, especially in the turbulent mixing environment of a large flume, can lead to cross-contamination. Pathogens and other microbial species are spread in the turbulently flowing liquid, and thus further transferred to other pieces of produce. In semi-batch and batch washing, the same tank of sanitizing liquid is typically used to wash many batches of produce, with the potential for considerable cross-contamination.
The need exists for a method to quickly and efficiently remove organic exudate, field debris, and soil particulates from freshly-cut produce while minimizing both the use of chlorine (or other sanitizers) and the volume of water used in the washing process, while (simultaneously) effectively cleaning the produce. In accordance with the current “inflight washing process,” immediately after the produce is cut, it is allowed to fall through a produce chute, such that as the produce descends, its fall is retarded by a generally upwardly flow of produce-washing liquid, and/or by a generally upwardly flow of air.
The upward flow of liquid and/or air causes the produce to reorient or tumble as it falls, and also retards the generally downward motion of the produce, thus increasing the exposure time to the liquid. These two factors, singly, or in combination, increase the likelihood that each part of each piece of produce is thoroughly washed and exposed to the sanitizing liquid.
Although the exposure time is relatively short, the reorienting “tumbling” motion of the freshly-cut produce as it falls through an upward flow of liquid and/or air leads to more effective produce sanitization than current industry practices. Further, after the falling produce lands, it can be quickly and effectively separated from the produce-washing liquid, which now includes dissolved and suspended organic exudate, field debris, and soil particulates.